Wireless communication systems have traditionally been used to carry voice traffic and low data rate non-voice traffic. Today wireless communication systems are being implemented that also carry high data rate (HDR) multimedia traffic, such as video, data, and other types of traffic. Multimedia Broadcast and Multicast Service (MBMS) channels may be used to transmit streaming applications, such as, radio broadcasts, television broadcasts, movies, and other types of audio or video content.
The multimedia broadcast multicast service (MBMS) is defined in a standard referred to as the 3rd Generation Partnership Project (3GPP) for Release 6. A standard TS22.146 defines high level service requirements of the MBMS, and the 3GPP standard TS22.246 defines typical service scenarios. MBMS services allow user equipment (UE) such as mobile telephones or other mobile terminals to receive services from service providers via the communications network. MBMS is a packet switch (PS) domain service for transferring multimedia data such as audio, pictures, video, etc, to a plurality of terminals using a unidirectional point-to-multipoint (PtM) bearer service.
Since MBMS is a multimedia service, multiple services of different quality of service (QoS) or multiple data sequences of different QoS in the same service may be provided to a single UE or to different UEs, and MBMS transmission mechanisms are needed that support variable source data-rates.
Because a channel is unidirectional, the UE generally does not communicate with a base station since allowing all subscriber units to communicate back to the base station might overload the communication system. Thus, in the context of PtM communication services, when there is an error in the information received by subscriber stations, the subscriber stations may not be able to communicate back to the base station. Consequently, other means of information protection can be desirable.
Among other considerations, transmission of a modulated information signal over a wireless communication channel requires selection of appropriate methods for protecting the information in the modulated signal. Such methods may comprise, for example, encoding, symbol repetition, interleaving, and other methods.
The characteristics and requirements for broadcast/multicast services are specified by 3GPP MBMS, and the related broadcast/multicast service layer functions. Simultaneous distribution of different content data may be required in a MBMS service; and simultaneous reception of more than one MBMS service for one terminal may be required, while MBMS transport services may vary for instance in QoS parameters. In such cases, unequal error protections (UEP) are naturally required to support various QoS of the high data rate communication for MBMS services in the wireless communications systems. Thereinafter, the data sequences with a higher quality requirement or/and a lower rate requirement are defined as the higher priority data, and the data sequences with a lower quality requirement or/and a higher rate requirement are defined as the lower priority data.
Traditionally, there have been two major types of methods of transmitting data applied for UEP. One method is to apply a more powerful conventional error-correcting code to the high priority data sequences. The other method of transmitting data is to use non-uniformly spaced modulation constellation, or hierarchical modulation to provide unequal protection for the data sequences with different priority levels. Coded modulation achieves both power-efficiency and bandwidth-efficiency by combining these two methods, seeing for example, “coded modulation with unequal error protection”, L.-F. Wei, et al., U.S. Pat. No. 5,105,442.
Another method of transmitting data combines coded modulation with time division multiplexing, each one of the classes of information being separately coded by using a conventional coded modulation scheme and then time-division-multiplexing the various coded outputs for transmission in different time-slots. An example of such a method can be seen in “multiplexed coded modulation with unequal error protection”, Hong Y. Chung, et, al., U.S. Pat. No. 5,214,656.
The above mentioned methods of transmitting data provide good performance of unbalanced data transmission; however have limited capacity due to their single transmit antenna configuration. Multiple-input multiple output (MIMO) communication systems employ multiple antennas at a transmitter and/or a receiver of the communication systems to improve coverage, quality, and capacity. Therefore one possible method to increase the capacity of such a communication system is to use multiple antennas to perform space-time (ST) processing. The conception of combining space-time processing with conventional UEP methods may be employed to achieve more capacity and better quality.
A method of transmitting data which concatenates forward error coding (FEC) with space-time coding (STC) is proposed for UEP in an MIMO system (see, “C. H. Kuo, etal., ‘Robust video transmission over wideband wireless channel using space-time coded OFDM system’, WCNC 2002, vol. 3. March 2002”.). Such a method provides more robustness to data sequences with higher priority levels by adopting more powerful FEC, while the embedded space time coding does not provide differentiation between data with different priorities. This kind of concatenation with the unified space-time processing cannot provide further differentiation between data sequences with different priority levels, thus limited QoS levels can be supported. And the implementation complexity of such a method of transmitting data is relative high, since for each priority input data sequence, a space-time coder is applied separately, and two antennas are necessary.
Some methods of transmitting data based on combining different space-time technologies were proposed for UEP in MIMO systems. See for examples, Muhammad Farooq Sabir, Robert W. Heath Jr, and Alan C. Bovik “An unequal error protection scheme for multiple input multiple output systems”, IEEE Asilomar Conference on Signals, Systems and Computers, vol 1, pp. 575-579, November 2002; and, C. H. Kuo, et al., “Embedded space-time coding for wireless broadcast with heterogeneous receivers”, Globecom 2000, vol 21, November, 2000. However these proposed methods need to change the coding structure of a space time coder for different protection requirements, and only specific rates, and specific protection ratios are provided when the space-time coders are selected, thus the drawback of the low flexibility and high complexity cannot be overcome.
There is therefore a need in the art for data transmission methods that will simultaneously support various QoS requirements in high rate data transmission of MBMS services at high system flexibility and low implementation complexity.